(a) Technical Field of the Invention
The present invention relates to an LED product, and more particularly to an LED scanning array driver chip and a regulation method capable of self-regulating brightness linear change.
(b) Description of the Prior Art
LED arrays are widely used as a man-machine interactive platform in many fields, such as consumer electronics of household appliances, industrial control, automotive electronics, medical equipment, and many other fields.
In some applications, all LEDs of the LED array are in the same color. LEDs are used to display characters, images, the running state of a machine, regulation of parameters and so on. In some applications, the LED array includes red, green and blue LEDs and uses a LED array driver chip to regulate the brightness of the red, green and blue LEDs to form various and adjustable colors. This application using LED array driver chip is a RGB LED. In some applications, the LED array includes both RGB LEDs and common LEDs.
In the system of these applications, LED arrays are usually used as the load of the LED array driver chip (hereinafter referred to the driver chip) to light or extinguish. MCU writes the control information of the LED array into the driver chip via serial communication protocols (the serial communication generally uses I2C, SPI communication, etc.) The driver chip controls the brightness and the current of the LED array according to the commands from MCU.
As shown in FIG. 1, the LED array comprises a plurality of LEDs. Each LED needs to control three basic parameters, a current value, a lighted state, an extinguished state. In specific applications, the brightness linearity of the LED is gradually decreased until it is extinguished. Or in an extinguished state, the brightness linearity is gradually increased unit a certain brightness and this brightness is kept. What is seen is that the LED is slowly darkened from the brighter state and finally it is extinguished, or it is slowly brightened from the extinguished state. The conversion of lighting and extinguishing the LED is not sudden, showing a soft brightness variation.
The linear change of the brightness of this LED is accomplished by changing the current of the LED constantly. The LED array is accomplished by means of scanning. For example, in a classic drive way, a driver chip has N IO buses to drive (N/2)2 LEDs; in an interconnected way, it can drive N (N−1) LEDs. Four IO buses are taken as an example. FIG. 2 shows a classic connection of the LED array. FIG. 3 shows an interconnection of the LED array.
As shown in FIG. 3, the brightness of each of LEDs 1-12 is different. Each LED is able to regulate brightness linearly. LED1 and LED2 are taken as an example to describe the problem that needs to be solved. As shown in FIG. 3, the brightness of the LEDs and the current passing through the LEDs are not a linear relationship, so the current passing through the LEDs is a non-linear change when the LED brightness varies linearly. As shown in FIG. 3, LED1 and LED2 have different brightness and current at the periods of T1 and T8. The brightness at the periods of T2, T3, T6, T7 is regulated linearly, not regulating the current linearly. A method to solve the above problem is that MCU via I2C, SPI or other communications constantly rewrites current control registers or PWM registers in the driver chip to change the current of the LEDs so as to control the brightness change of the LEDs. This will take up a lot of time resources of MCU to write the registers of the driver chip. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve this problem.